1. Field of the Invention
The present invention relates to a method of manufacturing an electronic component, and particularly relates to a method of manufacturing an electronic component having a high characteristic accuracy.
The present invention also relates to an electronic component, and particularly relates to an electronic component having a high characteristic accuracy.
2. Description of the Related Art
Improvement of the functionality and accuracy of an electronic device requires a high characteristic accuracy of an electronic component used in the electronic device. In particular, to achieve safety, a higher characteristic accuracy is required for an electronic component used in a medical or on-board electronic device. For example, an NTC thermistor is required to have a resistance value within a range of ±0.2% of a target resistance value or within a smaller range in some cases.
Japanese Patent Laid-Open No. 9-17607, Japanese Patent Laid-Open No. 8-236308, and Japanese Patent Laid-Open No. 2000-235904 each disclose a method of manufacturing a chip thermistor, the resistance value of which is adjusted at high accuracy.
In the method of manufacturing a thermistor disclosed in Japanese Patent Laid-Open No. 9-17607, the resistance value is adjusted as follows.
First, a plurality of ceramic green sheets on which internal-electrode conductive paste is printed in advance are laminated, and a plurality of ceramic green sheets on which no conductive paste is printed are laminated above and below the ceramic green sheets. Then, this laminated body is fired to obtain a ceramic element.
Subsequently, external-electrode conductive paste is applied and baked at both ends of the ceramic element to form baked external electrodes.
Subsequently, an initial resistance value between the baked external electrodes is measured to classify the ceramic element depending on the value.
Subsequently, for each classified ceramic element, part of the baked external electrodes and part of a ceramic part of the ceramic element are machined with different machining width and depth to obtain a resistance value within the allowable range of a target resistance value set in advance.
Subsequently, resin resistant against plating solution is applied on the machined part and cured to form an insulating resin film.
Subsequently, a plated external electrode is formed on each baked external electrode by plating, which completes manufacturing of a thermistor having a resistance value within the allowable range of the target resistance value. The insulating resin film is left intact as part of a product.
In the method of manufacturing a thermistor disclosed in Japanese Patent Laid-Open No. 8-236308, the resistance value is adjusted as follows.
First, a ceramic element is prepared.
Subsequently, conductive paste is applied on one of principal surfaces of the ceramic element to form one pair of facing surface electrodes (the surface electrodes are formed in a plurality of pairs in some cases). Conductive paste is applied at both end parts of the ceramic element to form one pair of external electrodes (terminal electrode). One of the surface electrodes is connected with one of the external electrodes, whereas the other surface electrode is connected with the other external electrode.
Subsequently, the ceramic element on which conductive paste is applied is fired to bake the surface electrodes and the external electrodes onto the ceramic element.
Subsequently, a leading end part of each of the surface electrodes formed on the one principal surface of the ceramic element is removed by barrel polishing or sandblasting to increase the distance between the facing surface electrodes, thus adjusting the resistance value. This completes manufacturing of a thermistor having a resistance value within the allowable range of a target resistance value.
Although Japanese Patent Laid-Open No. 8-236308 provides no detail on measurement of the resistance value along with the adjustment of the resistance value, the measurement can be performed as appropriate before or during the removal of the leading end part of each surface electrode.
In the method of manufacturing a thermistor disclosed in Japanese Patent Laid-Open No. 2000-235904, the resistance value is adjusted as follows.
First, a ceramic element is prepared. One pair of internal electrodes is buried inside the ceramic element.
Subsequently, conductive paste is applied and baked at both end parts of the ceramic element to form one pair of external electrodes. As a result, one of the internal electrodes is connected with one of the external electrodes, whereas the other internal electrode is connected with the other external electrode.
Subsequently, an initial resistance value between the external electrodes is measured to classify the ceramic element depending on the value.
Subsequently, a resist film that resistant to a solvent is formed on a surface of the ceramic element on which the external electrodes are formed. The resist film is formed in a cap shape at each end part of the ceramic element to cover the corresponding external electrode. Accordingly, part of a ceramic part of the ceramic element is externally exposed from the resist film.
Subsequently, the ceramic element on which the resist film is formed is immersed in a solvent of, for example, nitric acid, sulfuric acid, or phosphoric acid for a different time duration in accordance with the above-described classification depending on the initial resistance value. As a result, the ceramic part of the ceramic element exposed from the resist film is eroded. The depth of the erosion changes with the immersion time duration. The resistance value between the external electrodes of each ceramic element is adjusted to be within the allowable range of a target resistance value.
Subsequently, the resist film is removed, which completes manufacturing of a thermistor having a resistance value within the allowable range of the target resistance value.
However, the methods disclosed in Japanese Patent Laid-Open No. 9-17607, Japanese Patent Laid-Open No. 8-236308 and Japanese Patent Laid-Open No. 2000-235904, in which a characteristic value of an electronic component is adjusted, have the following problems.
First, in the method of adjusting a characteristic value (resistance value) of an electronic component disclosed in Japanese Patent Laid-Open No. 9-17607, after an initial characteristic value (initial resistance value) is measured, the classification is performed, and for each classified ceramic element, part of each baked external electrode and part of the ceramic part of the ceramic element are machined with different machining width and depth to obtain a characteristic value within the allowable range of a target characteristic value (target resistance value) set in advance. However, the machining of part of each baked external electrode and part of the ceramic part of the ceramic element is extremely cumbersome, which leads to a complicated and high-cost manufacturing process. Specifically, when the machining is to be performed by sandblasting, a protection film needs to be formed in advance on a region not to be machined so as to accurately machine a region to be machined. Then, after the sandblast is performed, the protection film needs to be removed.
In the method of adjusting a characteristic value of an electronic component disclosed in Japanese Patent Laid-Open No. 9-17607, after part of each baked external electrode and part of the ceramic part of the ceramic element are machined, resin resistant against a plating solution is applied on the machined part and cured to form an insulating resin film, and then a plated external electrode is formed on the baked external electrode by plating. This process of forming the resin film also leads to a cumbersome, complicated, and high-cost manufacturing process.
As described above, the method of adjusting a characteristic value of an electronic component disclosed in Japanese Patent Laid-Open No. 9-17607 leads to a cumbersome, complicated, and high-cost manufacturing process, and thus is not suitable for mass production for which high productivity is required.
In the method of adjusting a characteristic value (resistance value) of an electronic component disclosed in Japanese Patent Laid-Open No. 8-236308, the leading end part of each of one pair of surface electrodes formed on one of principal surfaces of the ceramic element is removed to increase the distance between the facing surface electrodes, thus adjusting the characteristic value. The distance between the surface electrodes is a factor largely affecting the characteristic value (resistance value). In the electronic component disclosed in Japanese Patent Laid-Open No. 8-236308, this important configuration is exposed on the surface of the ceramic element. Specifically, for example, any loss of the leading end part of a surface electrode when the electronic component is mounted after completely manufactured may potentially cause significant change of the characteristic value.
As described above, in the method of adjusting a characteristic value of an electronic component disclosed in Japanese Patent Laid-Open No. 8-236308, the characteristic value of the completed electronic component may potentially change, which results in manufacturing of an electronic component with low temporal characteristic reliability.
In the method of adjusting a characteristic value (resistance value) of an electronic component disclosed in Japanese Patent Laid-Open No. 2000-235904, the resist film is formed in a cap shape to cover the external electrodes, on the surface of the ceramic element on which the external electrodes are formed. Then, the ceramic element is immersed in a solvent of, for example, nitric acid, sulfuric acid, or phosphoric acid to erode the ceramic part of the ceramic element, thus adjusting the characteristic value. However, the adjustment of the characteristic value (resistance value) only through the erosion of the ceramic part without machining of the external electrodes typically requires a high amount (depth) of erosion of the ceramic part. However, when part of the ceramic part of the ceramic element is largely (deeply) eroded, the strength of the ceramic element is reduced. Specifically, the method of adjusting a characteristic value of an electronic component disclosed in Japanese Patent Laid-Open No. 2000-235904 potentially reduces the strength of a completed electronic component, which results in manufacturing of an electronic component with low strength reliability.
The method of adjusting a characteristic value of an electronic component disclosed in Japanese Patent Laid-Open No. 2000-235904 requires a process of forming, on the surface of the ceramic element, the resist film against a solvent, a process of eroding the ceramic part by immersing, in the solvent, the ceramic element on which the resist film is formed, and a process of removing the resist film, which leads to a cumbersome, complicated, and high-cost manufacturing process.
As described above, the method of adjusting a characteristic value of an electronic component disclosed in Japanese Patent Laid-Open No. 2000-235904 leads to reduced strength reliability of a completed electronic component, and also leads to a cumbersome, complicated, and high-cost manufacturing process.